Batteries are becoming such an organic part of modern life that my six-year-old daughter recommends changing the batteries when something breaks, and she alerts me immediately when the box pops up on the screen saying the battery is running out of energy. While materials researchers endeavor to find battery materials that can store more energy per unit weight and volume, the periodic table presents relatively few options for cost-effective solutions, so the control of batteries and the careful metering of their power and energy represent some of the more important research being done toward making them long-lived.
Christopher D. Rahn and Chao-Yang Wang explain methods and approaches to modeling batteries in Battery Systems Engineering. The philosophy of this book is that “fundamental model-based controllers have a built-in understanding of the underlying processes, allowing them to be more efficient, accurate and safe.” Most of the book is dedicated to battery model development at the cell and system levels, focusing on rechargeable batteries for hybrid electric vehicles.
Both Rahn and Wang are supremely qualified experts on the fundamental processes in batteries and relevant controls mathematics. Rahn is a professor of mechanical engineering at The Pennsylvania State University (Penn State), where he specializes in modeling electronic control systems for mechanical systems and leads the Mechatronics Research Laboratory. Wang is a Distinguished Professor of Mechanical Engineering and professor of materials science and engineering also at Penn State, and his research interests focus on the transport, materials, manufacturing, and modeling aspects of batteries and fuel cells. Rahn and Wang co-direct Penn State’s Battery and Energy Storage Technology (BEST) Center.
This book briefly tours the electrochemistry of batteries and then follows with mathematical methods for modeling such electrochemical systems. The models are built up from the fundamental processes in the batteries. The governing equations are presented for rechargeable batteries, based mainly on thermodynamics, reaction kinetics, and transport in porous electrodes and electrolyte, plus the impact of cell voltage, temperature, and aging. From there, the authors present 40 pages of discretization methods. Much of the same mathematical approaches are used in the chapter on system response. The chapter on battery systems models attempts to give fair balance to the several approaches, making clear that there are numerous ways to model the batteries and that estimation methods are still necessary. The last chapter is dedicated to battery management systems, with a top-level description of how one would build electronics around a battery for a car. Each chapter ends with questions and answers for readers to check their understanding of the book material.
By the end of the book, I had a hearty respect for the mathematical and modeling abilities of Rahn and Wang, but I did not have a solid feeling about how to use their methods in a simple hybrid system. For a practical prototype, much simpler models can be developed based on experimental polarization curves incorporated into relatively straightforward mathematical models. I also did not have a sense of how to use the modeling in the event that something went wrong with the battery—that is, it is unclear how to use the models to improve the longevity of the batteries or to make them safer. There is also no indication of how expensive the computational effort would be for running such detailed models.
A more accurate title for the book might be Battery Modeling for Hybrid Electric Vehicles as there is little practical systems engineering in the book. The detailed battery models would be very useful to people studying controls, and the methodology would be relevant to other electrochemical systems. The questions at the end of each chapter make it ideal for a graduate-level engineering controls class. The book would also be useful to battery materials scientists who are curious about how controls engineers work with their batteries.
Reviewer: Karen Swider Lyonsresearches fuel cell and battery materials and their integration into naval systems in Alexandria, Va., USA.
